The present invention relates to a thermoplastic resin composition, and more particularly, to a thermoplastic resin composition comprising an ethylene-vinyl alcohol copolymer and a modified polyester type thermoplastic elastomer which has an excellent compatibility with other resins, and exhibits a high gas-barrier property and an excellent impact strength as well as a good fluidity upon melting and, therefore, a good injection moldability. The present invention also relates to a multi-layer laminate comprising a layer comprising the above thermoplastic resin composition and at least one layers comprising a thermoplastic resin composition other than the above composition.
In general, ethylene-vinyl alcohol copolymer resins (hereinafter referred to merely as xe2x80x9cEVOH resinsxe2x80x9d) are thermoplastic resins having excellent oxygen impermeability and mechanical strength as well as good moldability and, therefore, have been extensively used in various applications such as films, sheets, materials for containers, textile fibers and pipes. However, the EVOH resins show a poor flexibility and especially are deteriorated in impact strength. In order to solve these problems, it has been conventionally attempted to enhance the stretchability and flexibility of molded products obtained from the EVOH resins by adding polyolefins thereto as described in Japanese Patent Application Laid-Open (KOKAI) Nos. 5-98084 and 2000-219792. However, according to the present inventors"" studies, it has been found that since such a composition is insufficient in compatibility between the EVOH resins and the polyolefins, the resultant molded products are not only still deteriorated in physical properties, reproducibility of appearance, and moldability, but also exhibits a considerably low gas-barrier property as compared to that of the EVOH resins, thereby failing to obtain satisfactory products.
On the other hand, it has been expected that polyester type thermoplastic elastomers having a good flexibility are widely used as alternate materials for vulcanized rubbers in various application fields. However, the polyester type thermoplastic elastomers are still insufficient in gas-barrier property such as oxygen impermeability in spite of good moldability and excellent low- and high-temperature characteristics thereof.
An object of the present invention is to provide a thermoplastic resin composition that is free from defects of both of the EVOH resins and polyester type thermoplastic elastomers, exhibits a high gas-barrier property, appropriate flexibility and impact resistance, a high toughness and a good injection moldability, and is capable of producing a molded product that is free from delamination of its surface layer.
Another object of the present invention is to provide a multi-layer laminate having a layer comprising the thermoplastic resin composition described above.
As a result of the present inventors"" earnest studies for solving the above problems, it has been found that the above objects can be achieved by such a resin composition comprising a specific modified polyester type thermoplastic elastomer and an EVOH resin. The present invention has been attained on the basis of the above finding.
To accomplish the aims, in a first aspect of the present invention, there is provided a thermoplastic resin composition comprising an ethylene-vinyl alcohol copolymer and a modified polyester-based thermoplastic elastomer produced by modifying a polyester-based thermoplastic elastomer with an unsaturated carboxylic acid or its derivative.
In a second aspect of the present invention, there is provided a multi-layer laminate comprising a layer A comprising the thermoplastic resin composition as defined in the first aspect, and at least one layer B comprising a thermoplastic resin composition other than the composition as defined in the first aspect which is laminated on one or both surfaces of the layer A.